Thermionic tube



M arch 7, 1939. H. H. ARlQlsfRoN e ET AL 2,149,656

THERMIONIC TUBE Filed Nov. 5, 1935 G H- 4 0E; 4 M n i 0v .5 #5 Y R WW M Z MW Patented Mar. 7, 1939 mamomc TUBE Harry Howard Armstrong and Arthur Burley Menefee, Beverly Hills, Calif., assignors to Tungsten Electrodeposit Corporation, Washington, D (1;, a corporation of Delaware 1 Application November 6, 1935, Serial No. 48,589

12 Claims.

This invention relates to improvements in electronic elements and more particularly to improved thermionic tubes.

The desi-derata in this particular field, that is to say in vacuum tubes, includes such features as high electronic emissivity, thermal resistivity and longevity. The typical vacuum tube of today, as is known, comprises an evacuated envelope containing an electron emitting electrode, a plate and a grid. Usually the electron emitting electrode or filament comprises thoriated tungsten. The elements tungsten and molybdenum are likewise found to be efficacious in the operation of vacuum tubes and, as is known, are employed quite generally in the fabrication of the filament and grid.

The choice of tungsten or thoriated tungsten for the electron emission element is in effect a compromise. It is known that certain substances, such for example as calcium, barium, thorium and the like are better thermionic emitters than metals such as tungsten, molybdenum and so forth. However, while calcium has a low work function and is a good emitter, it has a relatively high vapor pressure so thatmarked evaporation occurs at low temperatures. The use of the thoriated tungsten filament therefore involves a combination of a material having a relatively low emission but which is quite refractory and an element having a high emission. This combination is possible because of the fact that thorium is strongly adsorbed on the surface of tungsten even at the elevated operative temperatures of the vacuum tube.

We have found that improved electronic elements, and particularly thermionic tubes, may be produced by utilizing for the electrodes thereof substances which are provided with a special electrodeposited surface. According to the present invention such surfaces may be widely varied with respect to the components andhence with respect to the electronic or electrical characteristics so as to secure a wide range of desirable results.

More specifically considered, the invention comprehends the utilization for the elements of thermionic tubes of electrodeposited surfaces which comprisealloys of tungsten, molybdenum, tantalum, thorium and other similar refractory metals having the electrical characteristics which are desirable in this particular use.

As will be seen more fully hereinafter, the percentages of the respective components of the surface may be changed or modified within a wide permissive range to correspondingly modify the electrical characteristics of the surface. It will at once be seen that given the possibility of producing a surface including such refractory metals as tungsten, together with metals such as tantalum, which are not only refractory but vwhich have a desirably low work function, electron emitters of high efficiency are available.

In order more clearly to explain the invention a typical embodiment is shown in the accompanying drawing, in which:

Figure 1 is a conventionalized illustration of a typical vacuum tube.

Fig. 2 is an enlarged detail section of the filament. As shown in the drawing, the invention may be embodied in a vacuum tube comprising an evacuated envelope l which is formed with the usual base or ferrule 2 and the contacts 3. The tube may be a hard or soft tube and is producible by methods well known in the art. The effective operating elements of the tube include the filament 4, grid 5 and plate 6. The tube may also be formed with the usual screen 1. Such elements may be connected through suitable insulated leads to the contacts 3 in the manner well known to those skilled in the art.

In accordance with the invention one or more of these elements, such for example as the filament, plate or grid, may be formed with special electrodeposited surfaces of tungsten in combination with other metals so as to produce the desired electrical characteristics.

In carrying out the invention, for example, a tungsten nickel alloy may be electrodeposited upon a suitable base, such as ferruginous or nonferruginous wires or plates in accordance with the process described in our copending application Serial No. 744,566, filed September 18, 1934. Similarly the invention comprehends the employment as electron emitting surfaces: of special electrodeposited alloys containing such refractory and/or effective electron emitting metals as tungsten, tantalum, molybdenum and thorium. Desirable combinations of these metals may be electrodeposited in the form of an alloy upon a suitable base metal and utilized as filaments, grids or plates in electronic tubes. Such alloys may be employed either in binary form, such for example as an alloy or tungsten and tantalum, or in polynary alloy form in combination with other desirable metal components, such as thorium, nickel and the like.

As explained in co-pending application Serial No. 744,566, the respective percentages of the components of the electrodeposited alloy may be varied over a wide range. Such variations may be secured by modifying the initial metal ion concentration of the bath; the current density; temperature and the like. Thus operating under the disclosure, tungsten nickel alloys may be electrodeposited containing from 5 to 60% or more tungsten and the remainder nickel. For ordinary purposes where chemical and thermal resistance is desirable, alloys containing from approximately 25 to 40% tungsten are effective. The composition of the alloy may therefore be varied over a wide range, depending upon the particular results desired to be secured.

An effective method of producing elements of a thermionic tube comprises the utilization of an electrolyte, such for example as described in copending application Serial No. 14,372, filed April 2, 1935 and/or copending application Serial No. 28,187, filed June 24, 1935. Similarly, improved results, especially where the elements treated are desired to be used as filaments, may be secured by adding to the electrolytic bath a compound having a potentially available thorium ion so as to coplate or codeposit thorium in association with tungsten and/or tantalum and/or nickel. This may be done, for example, by adding a predetermined quantity of thorium to .the bifiuorid bath as described in copending application Serial No. 28,187. When an electric current is passed through such a bath it is found that there is plated out on the cathode a metallic surface containing an appreciable quantity of metallic thorium, in combination or alloyed with tungsten, nickel and tantalum. As disclosed in co-pending application Serial No. 28,187, the respective percentages of tungsten, tantalum and/ or nickel in a particular alloy may be widely varied by modifying such factors as the temperature of the bath, the current density, the initial metal ion concentration of the bath, the exposed area of corrodible anodes and the like. Electrodedeposited plates of tungsten, tantalum and nickel containing approximately 40% tungsten, 25% tantalum and 35% nickel have been produced. If desired, thepercentage of tantalum or tungsten may be increased or decreased above those mentioned by modification of the factors mentioned. The alloy stated operates effectively for the present purposes since it contains substantially 65% of such heavy refractory metals as tungsten and tantalum.

It will be appreciated, as has been explained in the copending applications referred to, that by the proper adjustment of temperature, hydrogen ion concentration and current density, the respective quantities of the several metals which are codeposited may be varied so as to secure any desired combination and thus insure a wide permissive range of electronic characteristics in the resultant plate. It is particularly to be observed that with this method of electrodepositing such refractory metals as tungsten, together with highly emissive metals, such as thorium and/or such metals as tantalum which are not only refractory but which also present a low work function, the electronic characteristics of an element may be advantageously modified or varied so as to secure a novel composite electrode having the characteristics desired for any particular use.

As intimated hereinbefore, the elements produced according to the present invention may be employed for the several elements of a hard or soft tube, such as the filament, grid, or plate. Depending upon the particular use to which the element is to be put, the electrolytic bath or the plating conditions may be modified so as to increase or decrease the respective quantity of an; particular component. By this process of coplating nickel, for example, with tungsten and tantalum, or of an alloy of nickel, tungsten, tantalum and thorium, and by the potentially variable composition of the plate, the physical characteristics of the elements may be controlled within a relatively wide range to thus impart to the element such features as improved ductility, tensile strength, thermal refractory characteristics and the like. Similarly the physical character of the resultant plate may be further modified by codepositing other metals, such as iron and cobalt, together with the refractory metals described.

It will likewise be appreciated that the special surfaces herein defined may be electrodeposited upon any suitable metal, such as ferrous or nonferrous bases. If desired the special surfaces may be plated upon pure tungsten or tungsten alloys, molybdenum or molybdenum alloys, or in fact upon any metal or alloy which functions effectively as a cathode in the electrolytic bath.

Likewise it is within the contemplation of the invention to specially treat the plated cathode prior to use as an element in a thermionic tube. For example a filament produced according to the present invention and which presents a surface containing such metals as tungsten, thorium and/ or tantalum may be flashed and heat treated at elevated temperatures so as to improve the emissive characteristics of the surface. It is to be observed that since the effective surface of the electrodes described herein comprise alloyed elements, offsetting is materially diminished.

It is to be observed that special electrodes, of differential cross-sectional characteristics, may be readily produced under the operations hereindescribed. As has been pointed out in the prior applications referred to, the respective quantities of the several components of the alloys may be varied, during a given plating operation, by modifying the temperature and/or currentdensity.

In this manner electrodes may be made up having:

a differential composition in cross-section. Thus, for example, electrodes may be produced by electro-codepositing nickel, thorium and/ or tantalum upon a suitable base, such as a tungsten base plate, and thereafter there may be electrodeposited on the plate an alloy of tungsten, tantalum and nickel. treated to insure the controlled diffusion of thorium through the element.

As noted above, operating under the principles of the present invention, elements for electronic tub-es may be produced having a wide variety of thermal and/or electrical characteristics fitting them especially effective for use as emitters, plates or grids.

While the invention has been described with respect to the special surface of the elements of a tube per se, that is to say the filament, grid, plate and the like, it is to be understood that if desired special surfaces may be electrodeposited upon the envelope itself, where such envelope is constructed of metal.

While preferred modifications of the invention have been described, it is to be understood that these are given didactioally merely for the purpose of explaining the underlying principles of the invention and not as limiting the invention to the specific illustrations set forth.

We claim:

1. An electronic tube element comprising a The element may be thereafter heat metallic base having an adherent electrodeposited surface consisting essentially of tungsten and thorium.

2. An electronic tube element comprising a suitable metallic base having an adherent electrodeposited surface consisting essentially of tungste and tantalum.

3. An electronic tube element comprising a suitable conducting base having an adherent electrodeposited refractory surface consisting essentially of tungsten, tantalum and thorium.

4. An electronic tube element comprising a suitable refractory conductive base on which is electrodeposited a surface consisting essentially of tungsten, nickel and thorium.

5. An electronic tub-e element comprising a refractory metal base having an adherent electrodeposited surface consisting essentially of tungsten, nickel and tantalum.

6. An electronic tube element comprising a refractory metal base having an adherent electrodeposited surface consisting essentially of tantalum and thorium,

7. An electronic tube element comprising a metal base having an adherent electrodeposited surface consisting essentially of predetermined percentages of tungsten, nickel, tantalum and thorium.

8. An emitter element for a thermionic tube which comprises a suitable metal base having an adherent electrodeposited surface consisting essentially of tungsten and thorium.

9. An electron emitting element for a thermionic tube which comprises a suitable metal base having an adherent electrodeposited surface which consists essentially of a preponderant amount of tungsten and a minor amount of thorium.

10. An electron emitting element for a thermionic tube which comprises a suitable metal base having an exposed surface consisting essentially of tungsten, tantalum and thorium.

11. An electron emitting element for a thermionic tube which comprises a suitable metal base having an adherent electrodeposited surface consisting essentially of tungsten, tantalum and thorium, said surface containing approximately 50% of tungsten.

12. An electron emitting element for thermionic tubes which comprises a suitable metal base having an adherent electrodeposited surface consisting essentially of tungsten and tantalum in the approximate ratio of two parts of tungsten to one part of tantalum.

I HARRY HOWARD ARMSTRONG.

ARTHUR BURLEY MENEFEE. 

